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Abstract

Infectious diarrhea is a major health hazard worldwide being responsible for several million deaths per year, especially in the developing countries (Leahy et al., 2005). Bifidobacteria and other lactic acid bacteria have been shown to exert protective effects against different pathogens causing acute diarrheal disease. In this study, the CD4+ T cell response during the course of Citrobacter rodentium infection was characterized. Moreover, the effect of pre-treatment with Bifidobacterium bifidum S17 on C. rodentium-induced colitis was investigated.
The presented results show that C. rodentium induces a strong CD4+ T cell response involving both Th1 and Th17 subpopulations with slightly higher contribution of Th17 cells. Pre-treatment with B. bifidum S17 supported clearance of C. rodentium at the resolving phase of infection. Furthermore, colonic hyperplasia was ameliorated in mice treated with B. bifidum S17 as indicated by significantly decreased colonic crypt length. Nevertheless, histological signs of inflammation and T cell responses triggered by C. rodentium infection were not affected by treatment with B. bifidum S17.
A red fluorescent C. rodentium was engineered and shown to be a useful tool for colonization studies in mice. Preliminary results obtained by confocal imaging indicated that C. rodentium was attached to the colonic mucosa in infected mice, and the numbers of attached C. rodentium was reduced in mice pre-treated with B. bifidum S17.
Collectively, the presented results suggest that B. bifidum S17 has some beneficial effect on C. rodentium-induced colitis. However, this effect is not related to changes in the inflammatory response but rather seems to be a more direct consequence of the reduction in C. rodentium counts during later stages of infection. The exact mechanism by which B. bifidum S17 exerts these effects remains to be elucidated in further studies.